|
Water Dimer
The water dimer consists of two water molecules loosely bound by a hydrogen bond. It is the smallest water cluster. Because it is the simplest model system for studying hydrogen bonding in water, it has been the target of many theoretical (and later experimental) studies that it has been called a "theoretical Guinea pig". Structure and properties The ab initio binding energy between the two water molecules is estimated to be 5-6 kcal/mol, although values between 3 and 8 have been obtained depending on the method. The experimentally measured dissociation energy (including nuclear quantum effects) of (H2O)2 and (D2O)2 are 3.16 ± 0.03 kcal/mol (13.22 ± 0.12 kJ/mol) and 3.56 ± 0.03 kcal/mol (14.88 ± 0.12 kJ/mol), respectively. The values are in excellent agreement with calculations. The O-O distance of the vibrational ground-state is experimentally measured at ca. 2.98 Å; the hydrogen bond is almost linear, but the angle with the plane of the acceptor molecule is about 57°. T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water (molecule)
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent). It is vital for all known forms of life, despite not providing food energy or organic micronutrients. Its chemical formula, , indicates that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. The hydrogen atoms are attached to the oxygen atom at an angle of 104.45°. In liquid form, is also called "water" at standard temperature and pressure. Because Earth's environment is relatively close to water's triple point, water exists on Earth as a solid, a liquid, and a gas. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds consist of suspended droplets of water and ice, its solid state. When finely divided, crystalline ice ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Bond
In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently bonded to a more Electronegativity, electronegative donor atom or group (Dn), interacts with another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Unlike simple Dipole–dipole attraction, dipole–dipole interactions, hydrogen bonding arises from charge transfer (nB → σ*AH), Atomic orbital, orbital interactions, and quantum mechanical Delocalized electron, delocalization, making it a resonance-assisted interaction rather than a mere electrostatic attraction. The general notation for hydrogen bonding is Dn−H···Ac, where the solid line represents a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are nitrogen (N), oxyg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Cluster
In chemistry, a water cluster is a discrete hydrogen bonded assembly or cluster chemistry, cluster of molecules of water (molecule), water. Many such clusters have been predicted by theoretical models (in silico), and some have been detected experimentally in various contexts such as ice, bulk liquid water, in the water vapor, gas phase, in dilute mixtures with non-polar solvents, and as water of hydrate, hydration in crystal lattices. The simplest example is the water dimer (H2O)2. Water clusters have been proposed as an explanation for some anomalous properties of water, properties of liquid water, such as its unusual variation of density with temperature. Water clusters are also implicated in the stabilization of certain supramolecular structures. They are expected to play a role also in the hydration of molecules and ions dissolved in water. Theoretical predictions Detailed water models predict the occurrence of water clusters, as configurations of water molecules whose tota ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ab Initio Quantum Chemistry Methods
''Ab initio'' quantum chemistry methods are a class of computational chemistry techniques based on quantum chemistry that aim to solve the electronic Schrödinger equation. ''Ab initio'' means "from first principles" or "from the beginning", meaning using only physical constants and the positions and number of electrons in the system as input. This ''ab initio'' approach contrasts with other computational methods that rely on empirical parameters or approximations. By solving this fundamental equation, ''ab initio'' methods seek to accurately predict various chemical properties, including electron densities, energies, and molecular structures. The ability to run these calculations has enabled theoretical chemists to solve a range of problems and their importance is highlighted by the awarding of the 1998 Nobel prize to John Pople and Walter Kohn. The term was first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ad Van Der Avoird
Ad van der Avoird (born 19 April 1943) is a Dutch theoretical chemist. He was professor of theoretical chemistry at the Radboud University Nijmegen. Education and career Van der Avoird was born on 19 April 1943 in Eindhoven. He studied at Eindhoven University of Technology, obtaining his PhD under George Schuit in 1968 with a thesis titled: ''"Perturbation theory for intermolecular forces : application to some adsorption models"''. He was professor of theoretical chemistry at the Radboud University Nijmegen and took up emeritus status in 2008 although he kept working. In 2013 Van der Avoird provided a theory on the relation between two benzene rings and their possible motion, the discovery was published with Gerard Meijer and a German research team in a paper in ''Angewandte Chemie''. The model solved a decade old scientific issue. Honors and awards On 25 April 2014 he was made a Knight in the Order of the Netherlands Lion, one of only fifteen appointees that year. Amongst other a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Abstracts Service
Chemical Abstracts Service (CAS) is a division of the American Chemical Society. It is a source of chemical information and is located in Columbus, Ohio, United States. Print periodicals ''Chemical Abstracts'' is a periodical index that provides numerous tools such as SciFinder as well as tagged keywords, summaries, indexes of disclosures, and structures of compounds in recently published scientific documents. Approximately 8,000 academic journal, journals, technical reports, dissertations, conference proceedings, and new books, available in at least 50 different languages, are monitored yearly, as are patent specifications from 27 countries and two international organizations. ''Chemical Abstracts'' ceased print publication on January 1, 2010. Databases The two principal databases that support the different products are CAplus and Registry. CAS References CAS References consists of bibliographic information and abstracts for all articles in chemical journals worldwide, and ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Forms Of Water
Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form may also refer to: *Form (document), a document (printed or electronic) with spaces in which to write or enter data *Form (architecture), a combination of external appearance, internal structure, and the unity of the design *Form (education), a class, set, or group of students * Form (religion), an academic term for prescriptions or norms on religious practice *Form, a shallow depression or flattened nest of grass used by a hare *Form, or rap sheet, slang for a criminal record People * Andrew Form, American film producer * Fluent Form, Australian rapper and hip hop musician Arts, entertainment, and media * Form (arts organisation), a Western Australian arts organisation * Form (visual art), a three-dimensional geometrical figure; one of the seven elements of art *Poetic form, a set of structural rules and patterns to which a poem may adhere *Mu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Water Chemistry
Water chemistry analyses are carried out to identify and quantify the chemical components and properties of water samples. The type and sensitivity of the analysis depends on the purpose of the analysis and the anticipated use of the water. Chemical water analysis is carried out on water used in industrial processes, on waste-water stream, on rivers and stream, on rainfall and on the sea. In all cases the results of the analysis provides information that can be used to make decisions or to provide re-assurance that conditions are as expected. The analytical parameters selected are chosen to be appropriate for the decision-making process or to establish acceptable normality. Water chemistry analysis is often the groundwork of studies of water quality, water pollution, pollution, hydrology and Hydrothermal vent, geothermal waters. Analytical methods routinely used can detect and measure all the natural elements and their inorganic compounds and a very wide range of organic chemical spe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cluster Chemistry
Nanoclusters are atomically precise, crystalline materials most often existing on the 0-2 nanometer scale. They are often considered kinetically stable intermediates that form during the synthesis of comparatively larger materials such as semiconductor and metallic nanocrystals. The majority of research conducted to study nanoclusters has focused on characterizing their crystal structures and understanding their role in the nucleation and growth mechanisms of larger materials. Materials can be categorized into three different regimes, namely bulk, nanoparticles and nanoclusters. Bulk metals are electrical conductors and good optical reflectors and metal nanoparticles display intense colors due to surface plasmon resonance. However, when the size of metal nanoclusters is further reduced to form a nanocluster, the band structure becomes discontinuous and breaks down into discrete energy levels, somewhat similar to the energy levels of molecules. This gives nanoclusters similar q ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
